Polyethylene terephthalate (hereinafter referred to as PET) fiber has been mass-produced throughout the world, to establish a large industry, because it is most suitable for the clothing use.
Polytrimethylene terephthalate (hereinafter referred to as PTT) fiber is known from prior art documents such as J. Polymer Science: Polymer Physics Edition: Vol. 14, p 263 to 274 (1976), Japanese Unexamined Patent Publication (Kokai) No. 52-5320 or WO-99/27168.
There is a disclosure in these prior art documents in that a fabric using PTT fibers having a proper elongation at break, thermal stress and/or shrinkage in boiling water has a low modulus to exhibit a soft hand touch and is suitable for the clothing such as inner wear, outer wear, sportswear, hosiery, lining cloth or swim suits.
On the other hand, polyester conjugate fibers of a side-by-side type or an eccentric sheath/core type have been known as fibers capable of providing a fabric with a bulkiness without being subjected to a false-twist texturing process.
As a PTT type conjugate fiber characterized by a soft hand touch, there is a conjugate fiber in which PTT is used as at least one of its components or a conjugate fiber in which PTTs having different inherent viscosities are used as both components (hereinafter, these are referred to as polyester type conjugate fibers), as disclosed in Japanese Examined Patent Publication (Kokoku) No. 43-19108, Japanese Unexamined Patent Publication (Kokai) Nos. 11-189923, 2000-239927, 2001-55634, EP 1059372, Japanese Unexamined Patent Publication No. 2001-131837, U.S. Pat. No. 6,306,499, WO 01/53573 or U.S. 2002-0025433. These prior art documents describe that the polyester type conjugate fiber is characterized by a soft hand touch and a favorable crimp developing property which characteristics are suitable for various stretch fabrics or bulky fabrics.
In general, when the polyester type conjugate fiber is produced by a melt spinning method, there are a two-stage method in which an undrawn fiber once wound as a package is drawn to be a drawn fiber and a single-stage method in which the spinning and the drawing are continuously carried out in one process.
In Japanese Unexamined Patent Publication (Kokai) Nos. 2001-131837, 2001-348734 and 2002-61031, a so-called direct spin-draw method is proposed when the polyester type conjugate fiber is produced, in which the spinning and the drawing are continuously carried out in one stage.
Particularly, in Japanese Unexamined Patent Publication No. 2001-131837, a polyester type drawn conjugate fiber is disclosed, which has a stretching elongation of 10% or more even under a load of 3.5×10−3 cN/dtex by controlling a thermal shrinkage stress thereof to be 0.25 cN/dtex or more. This polyester type drawn conjugate fiber can be hard-twisted and used for a woven fabric having a large structural-constraint force, in which fabric the fiber develops a high crimpability.
Methods for obtaining a pre-oriented fiber to be false-twisted are disclosed in Chemical Fibers International: Vol. 47. p72 to 74 (February, 1997), and Japanese Unexamined Patent Publication (Kokai) Nos. 2001-20136 and 2000-256918. In these documents, as a pre-orientated fiber to be false-twisted, a fiber consisting solely of PTT or a polyester type conjugate fiber is disclosed, which is wound at a speed of 2000 to 6000 m/min without using a godet roll or with a cold godet roll.
According to the study of the present inventors, the polyester type pre-oriented conjugate fiber or drawn conjugate fiber obtained at a high spinning speed has a high orientation degree but a low crystallinity. Such a pre-oriented conjugate fiber or drawn conjugate fiber has a glass transition temperature in a range from approximately 35 to 45° C. and is extremely sensitive to temperature and humidity.
In a spinning process, there is a phenomenon in that the heat generation of a motor of a winder running at a high speed is transmitted to a package via a bobbin shaft to increase the package temperature. Also, the package temperature rises by the heat generated due to the friction between the package and a presser roll. It has been also apparent that, if the package temperature is increased by such causes, the pre-oriented conjugate fiber or drawn conjugate fiber shrinks in the package during the winding.
The shrinkage of the pre-oriented conjugate fiber or drawn conjugate fiber hardly occurs in package-selvage portions (hereinafter referred merely to as selvage portions) in which the fiber is layered to have a high winding hardness, but solely occurs in the fiber layered in the remaining portion (hereinafter referred to as a central portion). As a result, the package is of a high-selvage shape during the winding. Once the high-selvage shape is formed, the selvage portion is alone in contact with the presser roll and the frictional heat is further concentrated to the selvage portion as a winding weight of the package increases.
The resultant package thus wound to have a predetermined diameter is of a so-called high-selvage shape wherein a (winding) diameter of the selvage portion is larger than that of the central portion. FIG. 1 is a schematic illustration of a package in a non-high-selvage shape, and FIG. 2 is a schematic illustration of a package in a high-selvage shape.
The high-selvage shaped package not only has a difference in diameter but also has a large difference in fiber property as described later, such as a thermal characteristic, yarn fineness and the number of crimps, between the selvage portion and the central portion.
In addition, as a winding weight increases, a lateral end surface of the package tends to be bulged outward due to the fiber shrinkage to form a so-called bulge whereby it is impossible to remove the package from the winder.
(i) Difference in Dry Heat Shrinkage Stress Value
The polyester type conjugate fibers in the selvage portion and the central portion of the package are different from each other in dry shrinkage stress value obtained by the measurement of the heat shrinkage stress described later. That is, the dry heat shrinkage stress value of the conjugate fiber in the selvage portion is higher than that of the conjugate fiber in the central portion.
It has been apparent that the difference in heat shrinkage characteristic becomes apparent as a difference in shrinkage or crimpability of a fabric during the dyeing process to cause a drawback of appearance quality such as a tight yarn or a puckering.
(ii) Variation in Yarn Fineness
The variation in yarn fineness of the pre-oriented conjugate fiber or drawn conjugate fiber is a periodic variation corresponding to a fiber length from one of the selvage portions of the package to the other (1 stroke or 2 strokes).
Charts measuring the variation in yarn fineness of the pre-oriented conjugate fiber or drawn conjugate fiber unwound from the package by an evenness tester are shown in FIGS. 3 and 4. FIG. 3 is a chart corresponding to the package of FIG. 1 and FIG. 4 is a chart corresponding to the package of FIG. 2. In the measurement charts, the periodic variation is observed by downward pin-like signals appearing at an equal pitch on a lower yarn fineness side. The existence of the downward signal means that a yarn fineness of the fiber (yarn thickness) at this point in the fiber length direction fluctuates to the smaller side.
It has been apparent that such a variation in yarn fineness causes a periodic dyeing unevenness in a false-twist textured yarn or a fabric.
(iii) Apparent Crimp
The polyester type conjugate fiber is characterized to have a latent crimpability capable of developing the crimp after the heat treatment. However, there may be a case in which the crimp has already been developed while the fiber is maintained as being wound in the package. This is the apparent crimp.
As the apparent crimp can cause a rise in the unwinding tension when the polyester conjugate fiber is unwound from the package at a high speed, it is preferably lowered.
As described before, it has been apparent that the polyester type conjugate fiber wound in the selvage portion of the package is liable to develop the apparent crimp in comparison with the fiber wound in the central portion.
For instance, there may be a case in which the apparent crimp exists in the selvage portion even if no apparent crimp exists in the central portion. When the polyester type conjugate fiber is unwound from such a package at a high speed, it has been apparent that the unwinding tension fluctuates due to apparent crimp to generate the yarn breakage during the false-twist texturing process or the weaving/knitting process.
(iv) High-speed Unwinding Property
A plain weave fabric represented by taffeta or twill or a warp knit fabric such as a tricot fabric is adopted for the clothing such as a lining cloth or a innerwear. Since a raw fiber not processed by a false-twist texturing or the like is often used for these fabrics, the arrangement of the fibers in the fabric is regular. Thus, there is a problem in that the drawback existing in the fiber is directly apparent as a fault in the fabric such as a streaky warp, a tight weft or a dyeing unevenness.
Recently, a cost competition has become severe in the weaving or knitting process and the processing speed has been higher in correspondence thereto. For example, a warping speed in the preparation of warp yarns for the woven fabric increases from the conventional range of from 100 to 200 m/min to a recent range of from 500 to 1000 m/min. Also, a weft-picking speed in the loom is as fast as in a range from 800 to 1500 m/min in an industrial process.
If the fluctuation of the unwinding tension corresponding to the yarn length from one end surface to the other end surface of the package is large during the unwinding of the polyester type conjugate fiber from the package at a high speed, the yarn breakage increases. Also, if the difference between the maximum value and the minimum value of the tension fluctuation (hereinafter referred to as the difference in unwinding tension) is large, a periodic quality fault occurs in the fabric, such as a tight yarn or others.
FIG. 7 is a chart showing a fluctuation of the the unwinding tension when the polyester type conjugate fiber is unwound at a high speed from the package having a favorable winding shape shown in FIG. 1. FIG. 8 is a chart showing a fluctuation of the unwinding tension when the polyester type conjugate fiber is unwound at a high speed from the package having an unfavorable winding shape shown in FIG. 2.
In FIGS. 7 and 8, a horizontal axis represents a yarn length of the polyester type conjugate fiber and a vertical axis represents an unwinding tension.
Accordingly, in any case when the polyester type conjugate fiber package having the above-mentioned drawbacks therein is used for the knitting or the weaving as it is without being drawn or when it is used for the knitting or the weaving after being drawn and false-twisted, the resultant dyed fabric generally is unfavorable in dyeing uniformity and exhibits a periodic unevenness of dyeing or luster. Thus, it has been apparent that the economical value of the fabric which is a final product is significantly deteriorated. Such a drawback cannot be solved even though the high-selvage shape of the package is eliminated to some extent.
Either of the packages disclosed in Japanese Unexamined Patent Publication (Kokai) Nos. 2001-131837 and 2001-348734 have the above-mentioned periodic drawbacks therein because the heat shrinkage of the conjugate fiber is large and the high-selvage shape is significant during the winding process.
Accordingly, there has been no polyester type conjugate fiber, obtained by the single-stage melt-spinning method in the prior art, which is capable of producing a fabric free from periodic dyeing unevenness, good in dyeing uniformity and excellent in dignity as well as no polyester type conjugate fiber package excellent in high-speed unwinding capability.